- client-go discovery clients constructed using `NewDiscoveryClientForConfig` or `NewDiscov...

  to deleted pods did not get cleaned up correctly, which could (among other things)
  cause DNS problems when DNS pods were restarted. ([#127780](https://github.com/kubernetes/kubernetes/pull/127780), [@danwinship](https://github.com/danwinship))

**Note**: This only impacts the cluster if the ServiceAccount admission plugin is used (most cluster should have this on by default as recommended in https://kubernetes.io/docs/reference/access-authn-authz/admission-controllers/#serviceaccount), the `kubernetes.io/enforce-mountable-secrets` annotation is used by a service account (this annotation is not added by default), and Pods are using ephemeral containers.

  * You can find out what taints you have in place on a node while you are still running Kubernetes 1.5 by doing `kubectl describe node <node name>`; the `Taints` section will show the taints you have in place. To see the taints that were created under 1.5 when you are running 1.6, do `kubectl get node <node name> -o yaml` and look for the "Annotation" section with the annotation key `scheduler....

- Using `--log-file` is known to be problematic in 1.15. This presents as things being logged multiple times to the same file. The behaviour and details of this issue, as well as some preliminary attempts at fixing it are documented [here](https://github.com/kubernetes/kubernetes/issues/78734#issuecomment-501372131)

## Urgent Upgrade Notes

### (No, really, you MUST read this before you upgrade)

#### API Machinery

- A deprecated flag `--pod-max-in-unschedulable-pods-duration` was initially planned to be removed in v1.26, but we had to change this plan. We found [an issue](https://github.com/kubernetes/kubernetes/issues/110175) in which Pods can be stuck in the unschedulable pod pool for 5 min, and using this flag is the only workaround for this issue. 

  
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- Kube-scheduler implements scheduling hints for the VolumeRestriction plugin.
  Scheduling hints allow the scheduler to retry scheduling Pods that were previously rejected by the VolumeRestriction plugin if a new pvc added, and the pvc belongs to pod. ([#125280](https://github.com/kubernetes/kubernetes/pull/125280), [@HirazawaUi](https://github.com/HirazawaUi)) [SIG Scheduling and Storage]
- Kube-scheduler implements scheduling hints for the VolumeZone plugin.

- The DRA device taints and toleration feature received a separate feature gate, `DRADeviceTaintRules`, which controlled support for `DeviceTaintRules`. This allowed disabling it while keeping `DRADeviceTaints` enabled so that tainting via `ResourceSlices` continued to work. ([#135068](https://github.com/kubernetes/kubernetes/pull/135068),...

- Topology Aware Hints now ignores unready endpoints when assigning hints. ([#106510](https://github.com/kubernetes/kubernetes/pull/106510), [@robscott](https://github.com/robscott))